/// <summary>
/// Returns the value of the probability distribution function.
/// </summary>
/// <param name="x">Value</param>
/// <returns>float precision floating point number</returns>
public float Distribution(float x)
{
if (x < 0)
{
return(float.NaN);
}
return(Special.GammaIncomplete(k, lambda * x) / Special.Factorial(k - 1));
}